Mount Prospect, Illinois 7 Day Weather Forecast

Wx Forecast - Wx Discussion - Wx Aviation

949
FXUS63 KLOT 271814
AFDLOT

Area Forecast Discussion
National Weather Service Chicago/Romeoville, IL
114 PM CDT Sat Jun 27 2026

.KEY MESSAGES...

- Dangerous heat is expected across the area next week.

- Afternoon heat index values forecasted over 100 degrees each
  day next week, with little to no relief at the lakeshore and
  at night.

&&

.DISCUSSION...
Issued at 114 PM CDT Sat Jun 27 2026

A weak area of low pressure, loosely analyzed in south central
Illinois, is taking its sweet time moving east. A pseudo warm
front along and just south of the southern portions of the
forecast area is the main focus of showery precipitation this
morning and afternoon. While the lingering moisture north of
this area will continue to feature a wide swatch of cumulus
clouds, most of the shower activity should remain confined to
the US 24 corridor, and diminish as sunset approaches.

Recent forecasts have been monitoring an incoming EML plume out
of the southern Plains tonight along an axis created by an
amplifying ridge/trough. Models are consistently trending more
hesitant with its northward progression due to lack of moisture
and forcing. While the forecast was kept dry through the night,
closer attention is being paid to what may transpire in South
Dakota tonight. That previously mentioned EML plume will drive a
fairly stout northwest to southeast oriented MUCAPE axis into
Sunday. There has been a notable uptick in model activity
developing a MCS in South Dakota tonight and have it moving
eastward. While it is a small percentage of models, some have it
riding the instability gradient southeastward into northwest
Illinois. For now, confidence is low in the threat for showers
or storms tomorrow afternoon. It would take a fairly strong MCS
to hold itself together and fight the drier air mass expected
over Illinois tomorrow, and even the models that show it
entering Illinois have it arriving in a decaying state. But with
plenty of instability and shear, PoPs were increased to at
least have "silent" 10 to 14 percent chances in the northern
half of the forecast area.

The main focus of the forecast will continue to be the first
heat wave of the year. The aforementioned amplifying upper level
pattern will continue today and tomorrow and feature a strong
upper level low to the west, and an upper level high embedded in
a ridge to the east. This pattern will advect around 25C
temperatures at 850 mb into the area and turn the prevailing
wind pattern to the southwest. This warmer, drier air mass is
expected to remain for much of next week. Widespread
temperatures in the 90s, and dew points well into the 70s will
create hot and humid conditions. This will create afternoon heat
index values around 105F each day starting on Monday. Little to
no relief can be expected at the lakeshore with the offshore
flow, and nighttime will not help either as overnight lows are
only expected in the mid to upper 70s. It is becoming
increasingly likely that a Heat Advisory will be needed across
the forecast area, but for the time being, an Excessive Heat
Watch was issued for Cook County from Monday afternoon through
Wednesday evening.

So, if confidence in an Advisory is increasing, why was one not
issued? Why did Cook County get a Watch? Is a Warning possible
for the rest of the forecast area? First, Cook County has a
different criteria for Heat watches and warnings, given the
population size. It only takes heat indices of 105F for
only two days or three days of 100F to justify a watch/warning.
The rest of the forecast area needs heat indices of 110F for a
watch/warning, and unless dew point temperatures over-perform,
that appears unlikely. Lastly, there is uncertainty with the MCS
tomorrow on its progression and if it lingers into Monday.
Additionally, models are trending farther east with the upper
level ridge and having it start to break down somewhere in the
middle of the week. This further adds questions on the duration
of the event, as a weaker and/or more eastern ridge would open
the door to additional convection that could provide lower heat
indices in the 90s and up to 100 (which is still hot, just sub-
criteria). Meanwhile, a stronger ridge could make for a longer
duration heat event that could last until the holiday weekend
next week.

So the main message: the first heat wave of the year is
expected next week. Take the hot temperatures into account when
planning activities through the week.

DK

&&

.AVIATION /18Z TAFS THROUGH 00Z MONDAY/...
Issued at 1216 PM CDT Sat Jun 27 2026

Northeasterly winds will prevail today and this evening, before
shifting out of the southeast on Sunday, likely becoming
sporadically gusty during the afternoon.

Largely VFR conditions are expected. Some MVFR cigs will be
possible near GYY this afternoon, followed by some shallow VFR
BR late tonight. Diurnal VFR cumulus will develop through the
day on Sunday. At ORD/MDW: low stratus continues to hug the
immediate lakeshore. There is a small chance this activity
attempts to ooze inland this evening, but currently not seeing a
significant signal for this and have maintained VFR conditions.

There is a very small (at this time less than 10 percent) chance
for a complex of thunderstorms originating out of Minnesota to
move into the region tomorrow afternoon. This does not appear to
be the most likely scenario as the environment will become
increasingly hostile to convection in the local area. Will
continue to monitor trends, but chances are much too low to
justify any precip mention in the extended ORD/MDW TAFs.

Carlaw

&&

.CLIMATE...
Issued at 252 AM CDT Sat Jun 27 2026

     .Daily Records for the Upcoming Week........

Chicago (KORD)
            Record High       Record Warm Minimum
June 29       97 (1954)            80 (1931)
June 30       99 (1953)            80 (2018)
July 1       103 (1956)            78 (1931)
July 2        99 (1970)            79 (1911)
July 3       102 (1949)            78 (1911)
July 4       102 (2012)            80 (1921)


Rockford (KRFD)
            Record High       Record Warm Minimum
June 29      103 (1931)            75 (1931)
June 30      102 (1931)            76 (2018)
July 1       101 (1931)            76 (1970)
July 2        99 (1910)            74 (1970)
July 3        99 (1925)            75 (2012)
July 4       102 (2012)            77 (1977)

NWS Chicago

&&

.LOT WATCHES/WARNINGS/ADVISORIES...
IL...Extreme Heat Watch from Monday afternoon through Wednesday
     evening for ILZ103-ILZ104-ILZ105.

IN...None.
LM...None.

&&

$$

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